Q: free download

Hello sadhan das,

Thanks for using Apple Support Communities.

As the article below states a payment source is required for already created Apple ID's for the first time they use the iTunes Store or App Store.  You are however able to change that payment type to "none" at a later time.

If you already have an Apple ID

If you already created your Apple ID, you need to add a payment method when you first use that Apple ID to sign in to the iTunes Store, App Store, or iBooks Store. But you can optionally remove the payment method after you sign in to the store. You won't be asked for a payment method again until you make your first purchase.

Create an iTunes Store, App Store, or iBooks Store account without a credit card or other payment method

http://support.apple.com/kb/HT2534

Take care,

Alex H.